PSA

The G surface protein of Paramecium primaurelia has important internal homologies and a periodic structure, which could be dictated in part by the rigid scaffolding of cysteine residues. The predicted secondary structure shows a quasi absence of alpha-helix and an abundance of beta-pleated sheets and random coils. The monotony of the amino acid sequence is in favour of a structural role for the protein [(PUBMED:3783679)]. This structure is based on the presence of 37 periods of about 75 residues, each period containing eight cysteine residues [(PUBMED:2308165)]. Homologies with other proteins are limited to surface antigens of trypanosomes.